In wireless communication systems, adaptive antenna arrays offer significant capacity and performance improvements, especially in interference-limited environment. This technology offers the ability to minimize same cell interference for mobile terminals being served simultaneously. It offers the prospect of a reduction of inter-cell interference. It also increases the signal-to-noise ratio of a particular mobile terminal being served and therefore enables an increase in user data rate. These benefits and advantages result in either higher data throughputs, or the ability to service more mobile terminals simultaneously, within a given cell or service infrastructure. This technology is generally referred to as smart antenna technology.
There is an ever-increasing demand on mobile wireless operators to provide voice and high-speed data services. At the same time, operators want to support more users per base station in order to reduce overall network cost and make the services affordable to subscribers. As a result, wireless systems that enable higher data rates and higher capacities have become very attractive. One way smart antennas technology has addressed this problem is advanced signal processing techniques called beamforming. This promising technology has already found its way into all the major wireless standards including 3GPP, 3GPP2, IEEE 802.16 and IEEE 802.11 systems.
There are two types of adaptive antenna array: diversity antenna array and beamforming antenna array. In a diversity antenna array, the data stream are coded in space and time and sent from multiple low-correlated antennas to achieve diversity gain. On the other hand, beamforming array utilizes the spatial directivity and provide beamforming gain. Spatial directivity requires a good correlation among antennas.
The multiple antennas of the array are typically deployed at the base station of each cell, and the signals transmitted or received by the antennas are combined with certain complex weights. Different antenna weights are used to extract the signals transmitted to or received from different mobile terminals within the cell. By properly adjusting the antenna beamforming weights, the multiple antennas can improve the signal-to-interference ratio (SIR) through beamforming.
With spatially separated antennas in the antenna array, beamforming becomes practical for both transmit and receive modes. Focusing radiant energy in the direction of a mobile terminal reduces the amount of overall power needed to be generated by the base station. Antenna array technology can be used to focus power coming from the mobile terminal to the base station via a reverse link or an uplink, as well as from the base station to the mobile terminal via a forward link or downlink.
Conventionally, the spatial signature detected in the most recently is used as a single basis for generating beamforming weights. The performance of the conventional communication systems with beamforming capability has been limited due to the impact of such issues as time varying channels and errors in channel computation. What is needed is an improved beamforming method for enhancing the performance of the wireless communications.